C Program to Concatenate Two Strings

In this example, you will learn to concatenate two strings manually without using the strcat() function.

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To understand this example, you should have the knowledge of the following C programming topics:

• C Arrays
• C Programming Strings
• C for Loop

As you know, the best way to concatenate two strings in C programming is by using the strcat() function. However, in this example, we will concatenate two strings manually.

Concatenate Two Strings Without Using strcat()

#include 
int main() {
  char s1[100] = "programming ", s2[] = "is awesome";
  int length, j;

  // store length of s1 in the length variable
  length = 0;
  while (s1[length] != '\0') {
    ++length;
  }

  // concatenate s2 to s1
  for (j = 0; s2[j] != '\0'; ++j, ++length) {
    s1[length] = s2[j];
  }

  // terminating the s1 string
  s1[length] = '\0';

  printf("After concatenation: ");
  puts(s1);

  return 0;
}

Output

After concatenation: programming is awesome

Here, two strings s1 and s2 and concatenated and the result is stored in s1.

It’s important to note that the length of s1 should be sufficient to hold the string after concatenation. If not, you may get unexpected output.