Arrays and Strings

String Compare

A character-by-character comparison decides whether two strings contain the same text.

compare loop The loop advances while characters match and neither string has ended.
equality result Two strings are equal only when both reach `'\0'` at the same position.

String Compare

useSecond
string_compare.c
Replay: real traced execution (multi-file project)
#include <stdio.h>

int sameText(const char left[], const char right[]) {
    int i = 0;
    while (left[i] != '\0' && right[i] != '\0') {
        if (left[i] != right[i]) {
            return 0;
        }
        i++;
    }
    return left[i] == right[i];
}

int main(void) {
    char first[] = "cat";
    char second[] = "car";
    char third[] = "cat";
    int useSecond = 0;

    const char *other = useSecond ? second : third;
    int same = sameText(first, other);

    printf("same=%d\n", same);
    return 0;
}

#include <stdio.h>

int sameText(const char left[], const char right[]) {
    int i = 0;
    while (left[i] != '\0' && right[i] != '\0') {
        if (left[i] != right[i]) {
            return 0;
        }
        i++;
    }
    return left[i] == right[i];
}

int main(void) {
    char first[] = "cat";
    char second[] = "car";
    char third[] = "cat";
    int useSecond = 1;

    const char *other = useSecond ? second : third;
    int same = sameText(first, other);

    printf("same=%d\n", same);
    return 0;
}

  1. first ← cat, second ← car, third ← cat, useSecond ← 0, other ← cat

    14int main(void) {15    char first→ cat[] = "cat";16    char second→ car[] = "car";17    char third→ cat[] = "cat";18    int useSecond→ 0 = 0; //@useSecond=11920    const char *other→ cat = useSecond0 ? secondcar : thirdcat;21    int same = sameText(firstcat, othercat);

  2. i ← 0

    3int sameText(const char leftcat[], const char rightcat[]) {4    int i→ 0 = 0;5    while (left[i] != '\0' && right[i] != '\0') {

  3. i ← 1

    pass 1 of 3
    4int i = 0;5while (left[i]c != '\0' && right[i]c != '\0') {6    if (left[i] != right[i]) {7        return 0;8    }9    i→ 1++;10}
    All 3 passes — pass 1 is the card above
    passleft[i]right[i]i
    1cc0 → 1
    2aa1 → 2
    3tt2 → 3

  4. return left[i] == right[i];

    10    }11    return left[i] == right[i];12}

  5. same ← 1

    20    const char *other = useSecond ? second : third;21    int same→ 1 = sameText(firstcat, othercat);2223    printf("same=%d\n", same1);24    return 0;25}
    outputsame=1

  1. first ← cat, second ← car, third ← cat, useSecond ← 1, other ← car

    14int main(void) {15    char first→ cat[] = "cat";16    char second→ car[] = "car";17    char third→ cat[] = "cat";18    int useSecond→ 1 = 1;1920    const char *other→ car = useSecond1 ? secondcar : thirdcat;21    int same = sameText(firstcat, othercar);

  2. i ← 0

    3int sameText(const char leftcat[], const char rightcar[]) {4    int i→ 0 = 0;5    while (left[i] != '\0' && right[i] != '\0') {

  3. i ← 1

    pass 1 of 3
    4int i = 0;5while (left[i]c != '\0' && right[i]c != '\0') {6    if (left[i] != right[i]) {7        return 0;8    }9    i→ 1++;10}
    All 3 passes — pass 1 is the card above
    passleft[i]right[i]i
    1cc0 → 1
    2aa1 → 2
    3tr—

  4. if (left[i] != right[i])

    5while (left[i] != '\0' && right[i] != '\0') {6    if (left[i]t != right[i]r) {7        return 0;8    }

  5. same ← 0

    20    const char *other = useSecond ? second : third;21    int same→ 0 = sameText(firstcat, othercar);2223    printf("same=%d\n", same0);24    return 0;25}
    outputsame=0